var a =function(strs){
  var strs =['abcdfe','abcjik','abckokd']

  if (strs ===nulll || strs.length ===0)
  {
      return ''
  }
  var str = str[0]
  for (var i=1;i<strs.length;i++)
  {
      for(j=0;j<str.length && j <strs[i].length;j++)
      {
          if(str.charAt[j] !== strs[i].charAt[j])
          {
              break
          }
      }
  }
  str =str .substring(0,j)
if(str === '')
{
    return
}
};
return str
var arr1=['叶陈辉','韦晴','陈杰','叶真','张宏','天翔','仕天','忠磊']
console.log(arr1.join(','));
var arr2='欢迎'
arr1.splice(13,0,'同学们')
console.log(arr1);
var arr3=arr2.concat(arr1)
console.log(arr3);
